Extracts an excerpt from text
that matches the first instance of phrase. The radius expands the excerpt on each
side of the first occurrence of phrase by the number of characters defined
in radius (which defaults to 100). If the excerpt radius
overflows the beginning or end of the text, then the excerpt_string will be
prepended/appended accordingly. If the phrase isn‘t found, nil is
returned.

Examples

excerpt('This is an example','an',5)# => "...s is an examp..."excerpt('This is an example','is',5)# => "This is an..."excerpt('This is an example','is')# => "This is an example"excerpt('This next thing is an example','ex',2)# => "...next t..."excerpt('This is also an example','an',8,'<chop> ')# => "<chop> is also an example"